Wisconsin 12-year-olds Morgan Geyser and Anissa Weier were charged as adults Monday for stabbing their 12-year-old friend on Saturday.

The girls say they were trying to kill the girl in homage to Slenderman—a fictional character on horror wiki Creepypasta.

Geyser and Weier told Waukesha County police that they believe Slenderman is real, and that murdering their friend would result in him revealing himself. They stabbed their classmate 19 times, but she survived.

The girls, who attend Horning Middle School together, went to Skateland Entertainment Center together Friday night to celebrate Geyser's birthday, then spent the night over at Geyser's house. Weier told police that she and Geyser planned to duct tape their friend's mouth and stab her in the neck that night, but decided to attack her the next day in a park instead.

On Saturday morning, the three girls went to David's Park, and played hide and seek in the woods. After tackling their classmate and pinning her to the ground, one or both of the girls stabbed their friend 19 times in the legs, arms, and torso.

Leaving the girl to die in the woods, Geyser and Weier began to walk towards the Nicolet National Forest, where they believe Slenderman lives.

Their victim made it out of the woods and onto a road, where she was found by a bicyclist. She was reported to in stable condition on Monday.

District Attorney Brad Schimel said that the attempted murder was plotted for months.

"It's troubling when a person lashes out in anger," he told the Journal Sentinel. "It's more troubling when they lash out in cold blood. Isn't that the worst kind of killer, the cold-blooded killer?"

The girls were charged with attempted first-degree murder, and each face up to 65 years in prison. They are each being held on $500,000 bond. If the case is moved to juvenile court, they could be imprisoned until they are 25 years old.